It is the first time YouGov has given UKIP, which campaigns for Britain's exit from the EU, the lead in the race to top the poll at the European elections on 22 May. Most previous polls have given the advantage to Labour by a few percentage points.

Slogan row

BNP leader Nick Griffin, who is standing for re-election to the European Parliament in the North-West of England, blamed what he claimed was biased reporting by the BBC for the collapse in support for his party, as well as the rise in support for UKIP.

"They (UKIP) are using all of our rhetoric, they are using our slogans, they are recycling our posters and people like it," he told BBC Radio 5 Live's Pienaar's Politics.

"The only difference is that UKIP won't deliver."

He said that unlike UKIP, which favours a reduction in immigration, the BNP's policy was to "shut the door - we don't want anyone, black brown, green or white".

UKIP came under fire earlier this year over its European election slogan "Love Britain, Vote UKIP", which is similar to a BNP slogan - Nigel Farage responded by saying it was "our slogan now".

The party has also faced a storm of criticism over a local council candidate, William Henwood, who suggested on Twitter that actor and comedian Lenny Henry should emigrate to a "black country".

'Desperation'

Mr Henwood, who is standing in a council election, made the comment on Twitter in response to a speech by Henry in which he said ethnic minorities were under-represented on British television.

But Neil Hamilton, who has been a senior figure in UKIP for some years and is standing as a local council candidate, said all parties had activists "who may have said something unpleasant on social media".

UKIP is the party of fear, saying be fearful vote for usNatalie Bennett, Green Party leader

He claimed Mr Griffin's comments "demonstrated that the BNP is a racist party and UKIP isn't".

But he agreed that UKIP was taking votes off the BNP, claiming "a lot of decent people" who were not racists had voted BNP in the past "out of desperation".

"They feel their communities are being swamped by immigrants from outside, whether they are from Eastern Europe or from other parts of the world.

"Now those people, the decent supporters of the BNP, from the last election, who weren't true BNP supporters at all, I am sure that quite a few of them are voting for a respectable alternative, which is UKIP."

Nigel Farage told The Guardian on Saturday that his party had taken all the votes it was likely to gain from Conservative supporters in the South of England and was now targeting Labour voters in the north, with the aim of pushing Ed Miliband into promising a referendum on Britain's membership of the EU.

'Murder'

But former Labour cabinet minister Peter Hain said: "I don't think Farage's success, which it's likely to be in a few weeks time, is going to affect Labour on the referendum at all."

He told the BBC's Andrew Marr show UKIP's rise had been "mainly at the expense of the Tories" but they were also "hoovering up" support from voters who were "fed up" with conventional politicians.

Green Party leader Natalie Bennett said her party was fighting the European elections as the anti-UKIP party.

"UKIP is the party of fear, saying be fearful - vote for us.

"We're saying hope for a better society, a society that works for the common good - so vote Green for that."

Lib Dem peer Dame Olly Grender said UKIP needed to be put under more scrutiny by the other parties, who she claimed were not taking the European elections seriously enough.

"I think what it (the European election) says about us as a nation is critically important and I think that UKIP are getting away with absolute murder," she told Pienaar's politics.